The present invention relates to a computed tomography system typified by an X-ray computed tomography system, and in particular, to a computed tomography system effective in increasing the image pickup efficiency of an image pickup system that only requires a testing object to be rotated in order to acquire data required to reconstruct images.
Owing to the history of development, some X-ray computed tomography systems use a 1st or 2nd generation image pickup system and others use a 3rd or 4th generation image pickup system. To acquire all the data required to reconstruct images, the 1st or 2nd generation image pickup system needs to translate and rotate a testing object. In contrast, the 3rd and 4th generation image pickup system has only to rotate the testing object. FIG. 4 schematically shows a conventional general configuration of a third-generation X-ray computed tomography system. The X-ray computed tomography system comprises an X-ray irradiation system 1, a turn table 2, and an X-ray detection system 3. The X-ray irradiation system 1, serving as a radiation irradiation system, irradiates a testing object M placed on the turn table 2 with an X-ray beam (in the illustrated example, a fan beam that fans out) 4 which serve as a radiation and which radiates in the direction of irradiation, the X-ray beam 4 having a predetermined region of irradiation. The spread of the region of irradiation with the X-ray fan beam 4 depends on the size of the X-ray detection system 3. The testing object M is irradiated with the X-ray fan beam 4 while being rotated relative to the X-ray irradiation system 1 and X-ray detection system 3 using the turn table 2. More specifically, the applied X-ray fan beam 4 is in the form of a pulse that synchronizes with a rotational position signal from the turn table 2. The pulse has a width of about 5 microseconds and an interval of, for example, about 5 milliseconds. An X-ray having penetrated the testing object M then enters the X-ray detection system 3. The X-ray detection system 3, serving as a radiation detection system, is composed of a plurality of X-ray detectors 5 linearly arranged at a predetermined pitch. Each of the X-ray detectors 5 detects the intensity of the X-ray. Each X-ray detector 5 outputs a signal corresponding to the detected intensity of the X-ray. Then, an image reconstruction system (not shown) executes an image reconstruction process on X-ray penetration data obtained on the basis of an output signal from each X-ray detector 5 to create a tomographic image of the testing object M.
Such an X-ray computed tomography system is based on an operation of picking up a tomographic image of one testing object placed on the turn table 2. Accordingly, when images of a plurality of testing objected are to be picked up, the corresponding amount of time is required for the image pickup. Thus, the X-ray computed tomography system does not operate efficiently when dealing with a large number of testing objects as in the case of, for example, product inspections on a production line.
Such a system as shown in FIG. 5 is known in connection with the improvement of the efficiency with which images of a plurality of testing objects are picked up. This system is applicable to the case in which the testing object M is sufficiently smaller than the turn table 2. That is, the fact that the testing object M is sufficiently smaller than the turn table 2 is utilized to place a plurality of testing objects M on the turn table 2 so that images of these testing objects M are simultaneously picked up. This makes it possible to reduce the time required to pick up an image of each testing object, thus improving image pickup efficiency.
Further, a system disclosed in JP-B-6-80420 is also known in connection with the improvement of the efficiency with which images of a plurality of testing objects are picked up. According to the system disclosed in JP-B-6-80420, a plurality of turn tables are installed in a direction in which testing objects are translated (linear reciprocation direction) so that images of the testing objects placed on the turn tables can be sequentially picked up. This improves the image pickup efficiency.
The image pickup efficiency improving system shown in FIG. 5 poses the following problem. The position of the testing object varies in the direction of irradiation with an X-ray as the turn table rotates. This results in an unwanted increase in the length of an X-ray path. As a result, the adverse effect of noise becomes more serious to degrade the quality of tomographic images. Further, when the number of testing objects placed on the turn table is increased in order to improve image pickup efficiency, it is unavoidable that during irradiation with an X-ray, one testing object is in the shadow of another, that is, an X-ray having penetrated one testing object penetrates another again. This also increases the length of the X-ray penetration path to make the adverse effect of noise more serious, thus degrading the quality of tomographic images. These problems can be avoided by increasing the intensity of the X-ray. However, this very disadvantageously increases the scale of the system. That is, in the system in which a plurality of testing objects are placed on one table to improve the image pickup efficiency, an attempt to increase image pickup precision disadvantageously results in an increase in the size of the system. In contrast, an attempt to avoid an increase in the scale of the system disadvantageously makes precise image pickup difficult.
On the other hand, the system disclosed in JP-B-6-80420 can avoid these problems. However, the system disclosed in JP-B-6-80420 is based on the 1st or 2nd generation system. Accordingly, the system disclosed in JP-B-6-80420 is effective on the 1st or 2nd generation system but is not expected to improve the image pickup efficiency of the 3rd or subsequent generation system.